1. Field of the Invention
The present invention relates to a rotary shock absorber and, more particularly, to a rotary shock absorber suitable for use in a suspension system of a vehicle.
2. Discussion of the Prior Art
An example of a rotary shock absorber for absorbing rotational force is disclosed in Japanese Utility Model Laid-Open No. 60-3336. As illustrated in FIG. 1, the rotary shock absorber is mainly composed of a cylindrical housing 1, a partition wall member 2 inwardly protruding in a radial direction from the inner surface of the housing 1, a rotary shaft 3 penetrating the housing 1, and a vane 4 fixed to the rotary shaft 3 for rotation herewith and extending in a radial direction so that the inner chamber of the housing 1 is divided into two chambers in which an operation fluid is filled. Further, the partition wall member 2 is formed with a communication pass 5, and an adjustable throttle valve 6 is disposed in the communication pass 5.
In the rotary shock absorber, the vane 4 is rotated in response to a rotation of the rotary shaft 3. With this rotation of the vane 4, the operation fluid in one chamber whose volume decreases flows to the other chamber whose volume increases through the throttle valve 6, which acts as a resistance against the flow of the operation fluid, whereby a damping force is generated. The damping force is adjusted by the throttle valve 6.
In the conventional shock absorber, since the damping force is generated by the fluid resistance of the throttle valve through which the operation fluid flows, the conventional shock absorber can provide neither sufficient damping force nor sufficient response speed.
Further, the damping force generated by the shock absorber increases in accordance with increase of the rotational speed of the rotary shaft 3, but has the same characteristic regardless of the rotational direction of the rotary shaft 3, as illustrated by solid lines A and B in FIG. 2. Therefore, the conventional rotary shock absorber is not suitable for use in a suspension system of a vehicle. Namely, a rotary shock absorber used in the suspension system is required to change its characteristic depending upon the rotational direction of the rotary shaft 3, as illustrated by broken lines C and D in FIG. 2. When the rotational shaft 3 rotates in a forward direction (rebound direction), it must generate a large damping force, as illustrated by the broken line C. On the contrary, when the rotational shaft 3 rotates in a reverse direction (bound direction), it must generate a relatively small damping force, as illustrated by the broken line D.
Further, in a conventional suspension system, dampers made of rubber are used as stoppers for limiting the bound and rebound movements of tires, and for absorbing shocks which are produced at the stroke ends. Although the shocks are almost absorbed by the dampers, it is desirable to reduce the shocks more to provide a comfortable ride.